1. Field of the Invention
The present invention relates to a method for well-posed magnetic imaging.
More particularly, the present invention relates to a well-posed magnetic imaging method that exploits a non-linear behavior of a characteristic time scale of the Néel relaxation for obtaining accurate high-spatial resolution images of magnetic tracers. The present invention also relates to new medical diagnostic instruments for characterization and imaging of vulnerable plaque.
2. Description of the Related Art
Magnetic relaxation of microscopic amounts of magnetic nanoparticles after switching off a magnetizing field can be measured very accurately using a superconducting quantum interference device (SQUID), the most sensitive and stable magnetic flux sensor. Weitschies et al. proposed magnetic relaxation immunoassay based on the magnetic relaxation of functionalized magnetic nanoparticles (MNP), where MNPs bound to biological targets (e.g., antibody, tissue, microorganisms etc.) were distinguished from unbound particles based on different relaxation times. The magnetic relaxation (MRX) technique has the advantages over other conventional techniques of being specific, quantitative, and sensitive in distinguishing between bound and unbound magnetic labels. This fact permits the use of a homogeneous assay, which does not require separation and removal of unbound MNPs. This technique has been extended for detection of magnetotactic bacteria, binding kinetics, cancer diagnosis, magnetically labeled immunoassay, drug localization, transplant rejection detection, hydrogel characterization, and dissipative heating in ferrofluids. By using a model system of liposomes, Chemla et al. demonstrated that the technique is sensitive enough to detect 5×104 nanoparticles by a SQUID sensor and discussed the possibility of obtaining a detection limit of 50-500 MNPs
The general theory of using MRX for imaging application was first proposed by Warzemann et al. and recently explored by others. But their approaches are practically restricted to a 2D image registration and have poor spatial resolution due to an inverse problem associated with transforming the data into a spatial image. Thus, there is a need in the art for a new direct magnetic relaxation imaging technique that exploits the non-linear behavior of the characteristic time scale of the Néel relaxation.